When carbon fibre mats are processed into formed parts, sewing threads are used to fix the mats. When the formed parts are trimmed, material pieces are generated which are not processed any further, but are recycled. During reprocessing, the sewing threads constitute an obstacle since they act as “predetermined breaking points”. On account of the sewing threads, these recycled fibres can only be used for applications of minor importance and are thus of little value. The sewing threads, i.e. also the connecting threads, do not consist of the same material as the carbon fibres of the mats.
It is obvious to use an optical sorter, e.g. CUBiSCAN, to sort out sewing threads having a different colour than carbon from a fibre and air stream. The drawback of this is that the recycled parts must be torn into small pieces. The threads are not detected and removed entirely.